The present invention relates to an electronic beam pattern drawing method, a production method of a molding die, a production method of moldings (molded product), and an electronic beam pattern drawing apparatus.
Conventionally, as an information recording medium, for example, CDs and DVDs are widely used. Then, many optical elements are used for a precision equipment such as a reading apparatus for reading these recording media. There are many cases where, for optical elements used for these equipments, for example, optical lenses, from a viewpoint of the cost reduction and size reduction, resin optical lenses rather than glass optical lenses are used. Such a resin optical lens is produced by a general injection molding, and also the molding die for the injection molding is formed by a general cutting processing.
In this connection, in the optical lenses, for example, an optical lens used for the reading apparatus having the interchangeability, in order to conduct the aberration correction, a fine structure of a diffractive grating structure such as a binary pattern or a blaze shape is formed.
When such a fine structure is formed, the fine structure is formed by cutting the molding die for the injection molding.
On the one hand, like as a recent pick-up lens for DVD, when the high density recording medium is read, there is a necessity to make the pattern of the diffractive grating more fine, therefore, it is necessary that the diffractive gratings of the binary pattern or blaze is made fine in a sub-micron order. As a method for drawing processing such a material, there is a limitation in the conventional cutting processing or laser processing. Therefore, the present inventor considers to use a method of optical exposure by the electronic beam.
In such a method, the electronic beam is irradiated by the electronic beam drawing apparatus onto the surface of the base material which is an original mold of the optical lens, and by scanning the beam in a predetermined drawing time period in a predetermined dose amount, the diffractive gratings of the binary pattern or blaze shape are drawn.
However, because the minimum dose resolving power of the dose amount of the electronic beam pattern drawing apparatus is determined by the minimum time resolving power of a D/A converter, the adjustment of the dose amount in such a electronic beam pattern drawing apparatus is conspicuously step-wise, when the drawing is conducted so as not to take a long period of time particularly by a high current value, and for example, when the diffractive structure such as the blaze shape is drawn, even when it is tried to form a smooth blaze inclination surface, by the difference of the resolving power of the minimum dose amount, the shape of the blaze inclination surface obtained after the drawing/development becomes step-wise.
The step-wise shape of the blaze inclination surface becomes a factor of the lowering of the optical characteristic of the optical lens, particularly a factor causing the lowering the diffraction efficiency, and further, when the quality of the products is considered, becomes a factor causing the lowering of the product value, therefore, in order together to increase the diffraction efficiency of the optical lens, with to increase also the product value, the necessity to form a smoother shape as possible is generated.
In view of the above problem, the present invention is made, and the first object is to provide an electronic beam drawing method, production method of the moldings, molding die to form moldings, and an electronic beam drawing apparatus which can suppress the step difference due to the minimum dose resolving power of the electronic beam drawing apparatus determined by the minimum time resolving power of the D/A converter and can form the smooth inclination surface.
Further, as an another problem, when the diffractive ring-shaped zonal structure of the binary pattern or blaze shape, is approximated by a polygon and drawn, as compared to a case where the diffractive ring-shaped zonal structure of the binary pattern or blaze shape is formed by an ideal circular pattern drawing, the lowering of optical characteristic of the optical lens, particularly, lowering of the diffraction efficiency are caused, further, because the portion of the joint of the drawing line in the apex of the polygon is conspicuous, when the quality of the products is considered, there is a problem that the products value is lowered from its appearance.
Accordingly, when the diffractive ring-shaped zonal structure of a binary pattern or a blaze shape, is approximated by a polygon and drawn, in order to avoid the problem of the lowering of diffraction efficiency of the optical lens generated due to this, or the problem of lowering of the product value, this is made close to an ideal circular pattern drawing as possible, and a necessity to contrive that the joint of the drawing line is made not conspicuous is generated.
In view of the above problems, the present invention is made, and the second object of the present invention is to provide an electronic beam drawing method, a production method of moldings, molding die to form the moldings, and an electronic beam drawing apparatus which can make close to a more ideal circular drawing, when the circular pattern is approximated by polygon and drawn.